My daughter had a ticket to Italy to visit a friend. She flew domestic to NYC and the airline would not allow her to board the international flight because her passport expired in 4 months. Subsequently she lost her airfare and acquired unforseen expenses with regard to local accommodations and transportation back to her hometown. IMO your partner needs to apply for an expedited passport, if that is possible.
I don't believe he *has to* have health insurance but it would be wise to have health insurance. Most people (not all) develope issues which require health care in their 60's and beyond. All one has to do is to look at the price health insurance premiums to see this is true. Additionally, what if he has an accident? Like a scooter accident? These are very common here.
If you go the 40K a month route, then you need to be aware of the exchange rate issue. Looks like you are an American and right now the dollar is very strong at about 36.6 THB for 1 USD. Will your pension convert to 40K a month if the dollar falls down to say 30 THB for 1 dollar, like it was a couple of years ago? I would also ask what your plans are for health care? If you are receiving a SS pension then you are more than likely in your 60's or older (unless you are younger & disabled) and I don't believe medicare will cover you over here. This means that you will need to buy private health insurance.
I was thinking about the concern you posted earlier about the agent adding themselves to the account. If you want to be certain that your name is the only name on the account, I'd open the account and make a small deposit (maybe 1K THB) then immediately go to another branch of the bank and ask the bank to verify how many signatories are on the account. Seems like an easy way to put your mind at ease before depositing 800K.